Add subscription_history to Namespace GraphQL Type

What does this MR do and why?

Initial discussions in !159933 (closed)

This is the last of a series of MRs to implement https://gitlab.com/gitlab-org/gitlab/-/issues/355985 as part of https://gitlab.com/groups/gitlab-org/-/epics/14290

Proof of Concept (to see the whole picture): !159045 (closed)

In this MR we:

1. Create Types::GitlabSubscriptions::SubscriptionHistoryType
2. Add subscription_history to EE::Types::NamespaceType using the above type
3. Add declarative_policy_subject to delegate the authorization to the namespace

MR Cadence

MR	description
!159901 (merged)	Add .by_namespace scope to GitlabSubscriptions::SubscriptionHistory
!159921 (merged)	Add relation between Namespace and GitlabSubscriptions::SubscriptionHistory
!159933 (closed)	👈 you're here

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

N/A

How to set up and validate locally

1. Switch to this MR's branch
2. Open GraphQL Explorer: https://gdk.test:3443/-/graphql-explorer
3. Run the following query:

   query getSubscriptionHistory(
           $fullPath: ID!
           $before: String
           $after: String
           $first: Int
           $last: Int
   ) {
     namespace(fullPath: $fullPath) {
       subscriptionHistory(after: $after, before: $before, first: $first, last: $last) {
         nodes {
           createdAt
           startDate
           endDate
           seats
           seatsInUse
           maxSeatsUsed
           changeType
         }
         pageInfo {
           hasNextPage
           hasPreviousPage
           startCursor
           endCursor
         }
      }
     }
   }
   
   ----- variables ----
   
   {
     "fullPath": "my-group-name",
     "first": 2
   }